Embryonic Connective Tissue

• Mesenchyme Tissue
  • Scattering of well separated cell
  • Relatively acellular with lots of ground substance
• Diagnostic Characteristics:
  • Cells are well spaced apart allowing other cells to migrate
  • Cells are still relatively close, tending to clump together compared to Mucoid CT
  • Fixed cell types are likely mesenchyme cells
  • Predominate fibers are probably collagen I

Umbilical Cord

• Contains 3 blood vessels:
  • 2 arteries and 1 vein
• Thin periphery “skin”
• All the rest of the tissue is mucoid connective tissue
• Function – carry blood and nutrients to fetus and waste products back
  • Don’t want it to kink
    • Put lots of proteoglycans which pull water, creating a slippery gel-like tension in the tissue
    • Allows umbilical to bend (still flexible) but hard to kink like a hose on pressure
• Diagnostic characteristics:
  • In reality, there aren’t extracellular fibers
    • Really participated proteoglycans like hyaluronic acid
  • Cells much more distantly spaced apart than in mesenchyme

Omentum

• Loose or Areolar CT
• This slide is stained for elastic fibers (not typically stained)
• Diagnostic characteristics
  • Scattered cells
  • Fibroblasts secrete fibers
    • Mast cells, eosinophils and macrophages probably there but can’t be distinguished because the stain doesn’t stain the cytoplasm and nuclei identification is not possible
  • Elastic fibers
    • Acute angle of intersection, very thin
    • Form a branching network but don’t branch themselves
  • Collagen fibers also present
    • Wide, unbranched straight fibers gathered in bundles
    • Fibers going in all directions (irregular) because it is unclear where the stress might be coming from

Trachea and Esophagus

• Plasma cells present in loose connective tissue
  • Diagnostic characteristics
    • Cartwheel nucleus pattern
    • Eccentrically located nucleus
• Plasma cells are derived from B cells

Auxiliary Skin

• Epithelium
  • Keratinized stratified squamous
• Glands
  • Simple cuboidal
  • Surrounded by loose CT
    • Less dense fibers, more cell nuclei than dense irregular CT
    • Loose CT to allow glands to expand when secreting
• Elastic Fibers
  • Allow dermis some stretch
  • Very dark staining but have acute intersections

Adipose Tissue

• White adipose cells
• Signet ring appearance due to unilocular appearance
  • Single lipid droplet

Heart

• Brown fat cells
  • For heat generation
  • Multilocular
    • Several lipid droplets in a cell
  • Most of it disappears in the first year of life

Tendon

• Dense regular CT
• Collagen fibers Type I with nuclei of fibroblasts throughout fasicle
  • Fibroblasts are very flat looking, stellite in shape
  • No cytoplasm visible
• Tendons don’t have a good blood supply
  • Take a long time to repair
• Muscle cells would have nuclei at the periphery and be striated
• Collagen is for strength
• Identify the tissue: dense regular connective tissue
• Identify the organ: tendon or ligament
  • Tendon – muscle to bone
  • Ligament – bone to bone

Liver

• Reticular fibers
  • Type III collagen (sugar coated)
  • Diagnostic characteristics:
    • Right angle intersections of interconnecting fibers
    • Squiggly, fairly short
    • Dark staining (silver)
  • Probably hard to find a reticular cell
• Nuclei are wandering cells (macrophages, lymphocytes, plasma cells)

Ligamentum Nuchae

• Elastic fibers
  • Branches in acute angles
  • Surrounded by amorphous ground substance and some collagen
• Nuclei are fibroblasts

Aorta

• Elastic CT
• Individual sheets of elastic fibers
  • Interconnected by finer elastic fibers in between
  • Collagen fibers are also found in between
• In this case, extracellular fibers secreted by the smooth muscle cells